1. Field of the Invention
This invention relates to a magnetic tape cassette, and more particularly to a magnetic tape cassette which has a magnetic tape received therein, such as a digital audio tape which is used to record a digital signal such as a (pulse code modulation) PCM signal thereon and reproduce it.
2. Description of the Prior Art
Recently, a PCM recording and reproducing apparatus has been proposed which is adapted to convert an analog signal such as an acoustic signal or the like into a digital signal such as a PCM signal, record it on a magnetic tape and reproduce it from the tape. Typically, such conventional PCM recording and reproducing apparatus is generally constructed to obtain a relatively high recording density by means of a rotation head. In the apparatus, a recording or reproducing operation is carried out by drawing out a magnetic tape from a magnetic tape cassette and winding it on the rotation drum on which the rotation head is provided.
A conventional magnetic tape cassette used in the PCM recording and reproducing apparatus fails to reproduce a signal recorded on a magnetic tape when a fingerprint or any foreign matter such as dust or the like is left thereon. In order to prevent such a problem, it is necessary to sealedly receive the magnetic tape in the cassette as much as possible. Also, it is necessary to provide the cassette with a space sufficient enough to insert a guide of a cassette deck or the like in the cassette, said guide serving to draw out the magnetic tape from the cassette during a recording or reproducing operation.
For this purpose, the conventional magnetic tape cassette includes a casing consisting of an upper and lower casing member in which a pair of reel hubs on which a magnetic tape is wound are rotatably housed. The reel hubs are each formed at a portion thereof above the magnetic tape wound thereon with a lock which is engaged with a hub brake arranged in the casing so as to be slidable in a direction perpendicular to a line defined by connecting axes of the reel hubs. The magnetic tape cassette also includes a slider arranged on the outside of the lower casing member so as to be slidable in the longitudinal direction of the casing to open or close a space defined in the casing for inserting a guide of a cassette deck therein and a front cover pivotally mounted on the casing so as to be pivotally moved due to movement of the slider to open or close a front portion of the casing.
In the conventional magnetic tape cassette constructed as described above, the front cover is pivotally moved about 90 degrees from the front portion of the casing to the upper casing member, so that the magnetic tape may be exposed at the front portion of the casing and the slider may be rearwardly moved to open the space for inserting the guide of the cassette deck therein. During non-use of the magnetic tape cassette, the slider and front cover cooperate with the casing to sealedly receive the magnetic tape in the casing and the hub brake is positioned so that a projection provided at each arm thereof may be ready for engagement with an engagement element provided on an inner surface of the front cover to cause the hub brake to be disengaged from the locks when the front cover is pivotally moved again. Also, during non-use the cassette prevents the reel hubs from being moved, thus preventing damage of the magnetic tape due to slack or bending.
In the conventional magnetic tape cassette constructed as described above and as shown in FIGS. 1 and 2, the hub brake 100 is provided with an engagement element comprising a recess 102 for holding a hub brake spring or double torsion spring 104 and pressing elements 106 inwardly projecting from the recess 102. However, such construction causes a part of a wall of the hub brake 100 to be substantially thin, resulting in deformation of the hub brake due to force applied thereto from the spring 104 or a variation in temperature, and makes the operation of assembling the hub brake 100 and inserting the hub brake spring 104 into the hub brake 100 highly troublesome.
Further, the above-described construction of the hub brake 100 causes pressure from the hub brake 104 to be applied to the hub brake 100 prior to the operation of combining the upper and lower casing members 108 and 110 together. This causes the reel hub 112 to be inclined or lifted as shown in FIG. 3, resulting in the lock 114 formed on the reel hub 112 interfering with a guide rib 116 formed on an inner surface of the upper casing member 108, thus making the combining together of the upper casing member 108 and the lower casing member 110 troublesome or highly difficult. Further, use of the hub brake spring 104 having strong force often causes damage to the hub brake 100 and/or reel hub 112 during assembling or operation.
Accordingly, it would be highly desirable to develop a magnetic tape cassette which is capable of constantly carrying out satisfactory operation for a long period of time and capable of being readily manufactured and assembled.